1. Field of the Invention
This invention relates to apparatus for cooling electronic components, and, more particularly, to such apparatus including one or more locally mounted fan units directing air to move along surfaces of a heat sink.
2. Summary of the Background Art
Many electronic devices, including laptop computers and workstations, are being designed with structures including heat sinks and fans for cooling individual circuit modules. Such a conventional cooling structures typically includes an axial-flow fan attached to extend horizontally along the top of a heat sink, which is in turn mounted to extend upward from the circuit module being cooled. The airflow from the fan is directed downward among cooling fins of the heat sink to make a 90-degree turn upon impinging upon the body of the heat sink, from which the fins extend upward, with heated air then flowing outward around the periphery of the heat sink. Problems associated with this conventional approach include a pressure drop that is created when the airflow impinges on the body of the heat sink, due to an associated reduction in the rate of airflow, and due to the fact that heated air is exhausted outward from the periphery of the heat sink. Often, additional critical components cannot be placed on the circuit board near the heat sink because of the presence of heated air. Thus, what is needed is a component cooling system that takes air from a space above the components and that returns heated air to the space above the components.
U.S. Pat. No. 6,664,673 describes a cooler for electronic devices comprising a heat exchange element, a rotor including an axial-flow fan and a blower with a radial impeller, and an electric drive rotating the rotor. Cooling air is driven downward by the axial flow fan past a number of heat sink surfaces, extending upward as pillars from the heat sink body. Then, from this central area, air is driven outward by the radial impeller, past a number of heat sink surfaces extending around the radial impeller, and outward from the periphery of the heat sink. Certain versions include a duct extending around this periphery, so that air is directed outward only from one end of the heat sink. One problem associated with this method is the space taken up along the circuit board, with space being provided for the radial impeller. Additionally, what is still needed is a component cooling system that returns heated air to the space above the components.
U.S. Pat. No. 6,367,542 describes a cooling assembly including a heat sink, an internal fan, a fan frame, and an external fan. The heat sink includes a base and a fin member attached to the base. The fin member includes a central portion and a plurality of fins extending radially from the central portion. A central cavity is defined in the fin member, surrounded by the fins. The internal fan is received in the central cavity to be supported by the central portion at the bottom of the cavity. The fan frame has an opening defined therein, and is mounted on the heat sink, with the external fan being mounted on the fan frame to cover the opening. Cooling air enters the external fan and is into the cavity. The internal fan accelerates airflow from upper portions of the fin member to lower portions thereof. The air then exits around the periphery of the heat sink. Again, what is needed is a cooling system that returns heated air to the space above the components.
U.S. Pat. App. Pub. No. 2003/0021679 describes a fan structure used with a heat sink, with the fan structure including an axle having first and second fan members at opposite ends, with blades of the two fan structures being angled in opposite directions. The first fan member is installed to extend along the top of the heat sink, while the second fan member is embedded into the heat sink. The heat sink includes an outer portion, in which fins extend, and an inner portion, connected to the outer portion through slots at the bottom at the inner portion and through an opening at the top of the inner portion, between the first and second fans. Heated air is pushed outward through a slot extending around the outer portion. Again, what is needed is a cooling system that returns heated air to the space above the components.
Other examples of the patent literature describe pairs of cooling fans installed in line with one another so that the output air from a first fan is directed to the input of a second fan. For example, U.S. Pat. No. 6,537,019 describes such a pair of fans rotating in opposite directions, with blades being angled in opposite directions, and with axes of rotation being aligned or slightly offset. U.S. Pat. No. 6,343,014 describes such fans as being mounted on a heat sink, separated by a spacer, and connected in series. U.S. Pat. App. Pub. No. 2002/0170703 describes such a pair of fans in which the fans are controlled in series, with the first fan being controlled by a first control circuit, and the second fan being controlled by a second control circuit, so that the second control circuit increases the speed of the second fan when the first fan fails. U.S. Pat. App. Pub. No. 2002/0167798 describes a heat-dissipating assembly including a heat sink having a base in contact with a surface of a heat-generating device and a plurality of fins extending upwards from the base, and a first fan and a second fan respectively disposed on a first position and a second position of the heat sink.
Other patents describe cooling fans being mounted in a side-by-side configuration. For example, U.S. Pat. No. 5,953,209 describes a pair of fans mounted side-by-side on a heat sink mounted in turn on an electronic cartridge, with one of the fans pushing air into the heat sink while the other fan pulls air out of the heat sink. U.S. Pat. No. 6,172,416 describes apparatus including a plurality of fans mounted to blow air along a heat sink substrate to cool a plurality of electronic devices. Adjacent fans may move air in the same direction or in opposite directions, with the heat sink substrate additionally providing electromagnetic shielding. U.S. Pat. No. 6,181,556 describes a thermally coupled heat-dissipation apparatus surrounding a solid-state electronic device or a thermal transfer column extending upward from a main board socketed device. What is needed is a relatively small cooling system for cooling a single electronic device while occupying a minimum space on the circuit card.
Japanese Patent No. 2001291983 describes a low cooling system for use within a notebook computer, where space above a circuit board is particularly limited. The cooling system includes two fans having rotary impellers, mounted side by side within a duct of limited thickness, producing airflow in a common direction, particularly in an area between the fans.
The patent literature includes other examples of devices including fans and heat sinks to solve problems that are more specific. For example, U.S. Pat. App. Pub. No. describes apparatus for cooling electronic components on a plug-in circuit board within an enclosure. Air is drawn from along an edge of the card by a single fan, to be driven past a high-energy power dissipating device, such as a graphical processor unit and over arrays of memory chips. U.S. Pat. App. Pub. No. 2003/0030980 describes a thermo-electro subassembly including a gas supply, a first duct, a first heat sink adjacent a first device, a second duct, and a second heart sink adjacent a second device. The gas supply may be realized as a fan, a blower, or a source of compressed gas.